Presented By

Lorenzo Andrioli

Thermal Analysis in Support to Thermal Protection System Seals

and Interface Design of IXVLorenzo Andrioli, Massimo Antonacci

Thales Alenia Space – Turin, Italy

Alessandro Mannarelli SSE Sofiter System Engineering – Turin, Italy

Thermal & Fluids Analysis WorkshopTFAWS 2011August 15-19, 2011NASA Langley Research CenterNewport News, VA

TFAWS Paper Session

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Outline

• Introduction• Analysis Approach• Interfaces (I/F) Thermal Mathematical Models

(TMMs) general description– Thermal network basic concept– Environment simulation– Analysis work logic– Model example

• New approach for Thermal Protection System (TPS) thermal analysis

• Summary & Conclusions

Introduction

Windward

Lateral

Nose

Flaps

Leeward

The IXV (Intermediate eXperimental Vehicle)

• An atmospheric re-entry demonstrator which will perform a suborbital flight and will re-enter in the atmosphere.

• To be launched by the ESA/Vega from the Centre Spatial Guyanais (CSG)

• It will experience the typical Low Earth Orbit re-entry thermal loads.

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Introduction

Main objective:

To develop an analytical approach to be implemented for I/F design of IXV.

Model characteristics changes operated by means of:– algorithms

– configurations

To properly simulate behaviour of items characterized by different:– thermal properties

– thermo-mechanical properties

– permeability

Leading to different temperature requirement limits.

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Interfaces (I/F)

External critical regions in which environmental agents can find a preferential way to dangerously affect internal environment and items.

Design requirements:

• to limit sneak flow and act as thermal barriers (proper sealing);

• to limit discontinuities (steps, gaps, and bowing) in the vehicle Outer Mould Line;

Introduction

• to allow depressurization and repressurization of IXV and TPS&H/S Assemblies.

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Introduction

Different types of I/Fs to be designed:• among different-type Thermal Protection Systems:

– nose-to-windward– nose-to-leeward– leeward-to-windward– windward-to-hinge– hinge-to-rear– hinge-to-leeward

• between TPSs and other subsystems:– floatation system ejectable panels insulation– venting hole– protection insulation over antennas– bridle channels insulation– protection insulation on umbilical mechanisms

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Analysis Approach

Modeling criterion• ESATAN Thermal

Lumped Parameter (TLP) solver

• Technique resembles System Thermal Mathematical Model (TMM) one improving temperature mapping capabilities

• highly customizable 2D mesh models and one 3D axisymmetric model

• depending on the I/F type, a fluid leak (sneak flow) through sealing materials is simulated

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I/F TMMs general description

Thermal network basic concept• Thermal network organized in node blocks linked

together to establish a geometrical hierarchy → propagation of changes by acting upon relevant parameters (e.g. modification of items sizing, material properties, etc.)

• Node blocks wrapped into arithmetical nodes→ spreading effect of surface heat exchanges implicitly solved (reliable evaluation of I/F temperatures)

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I/F TMMs general description

Environment simulation• Internal environment: radiative and convective

equivalent conductors (representative nodes defined on the basis of System TMM)

• External environment: radiative conductors and heat fluxes (ATDB, max heat load trajectory) or input from dedicated thermo-ablative software

• Sneak flow: modelled by means of a heat contribution calculated as:

)( / SCAIRIMPINGINGAIRpFLOWSNEAK TTcmQ

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I/F TMMs general description

Air mass flow: calculated with Darcy law 1D formulation

mGap

Seal thickness

phigh plow

th

pkAm

k permeability of the seal

air kinematic viscosity

air density

Sneak flow into non-passing through slots: air filling the gap is considered as stagnating (really thin and deep slots, highly conservative boundary layer temperature)

th spatial term describing the flow path (seal thickness)

p pressure

A flow area (gap × slot width)

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• Air flow through venting hole: equivalent thermal conductor (h × A) linking duct with a inflow boundary node

I/F TMMs general description

bush

air

r

kNuh

2

kair air conductivity

rbush duct internal radius

Nu Nusselt number

1Pr8

7.121

Pr1000Re

83

2f

fNu

264.1Reln79.0

1

f

From Petukhov-Gnielinski semi-empiric correlation:

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I/F TMMs general description

Analysis work logic

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I/F TMMs general description

Model example: typical TPS-to-TPS junction I/F

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Analysis results and their application

Local vs System TMMs T are applied to overall vehicle temperature maps all along the I/Fs envelope at C/S and TPS level.

Temperature maps are used as an input for System Thermo-elastic analyses → overall steps and gaps requirements verification

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New approach for TPS thermal analysis

Current approach modeling (ESATAN) flaws:• ESATAN-TMS GUI is in early development phase

→ code is usually written down by hand• Manual debugging and subroutine generation is the rule

→ coding is more error-prone than a robust front-end approach

• CAD interfacing tools are under development→ geometry is user discretized and modeled, usually in scripting form with graphic visualization

• Data exchange is manually managed by means of properly written routines→ a coding endeavor is required

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New approach for TPS thermal analysis

Solution: switching to an hybrid approach tool.

• Bi-directional from/to CAD geometry interfacing, with direct user intervention for simplification purposes

• Finite element based model mesh generation

• Possibility to chose between a Finite Element Method (FEM) or a TLP solution

• Possibility to chose between FEM or TLP like postprocessing (temperatures interpolated over the node vs isothermal nodes)

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New approach for TPS thermal analysis

FEM-TLP hybrid workflow in NX environmentAn example of hybrid approach workflow applied to a preliminary TPS-to-TPS I/F analysis.

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Summary & Conclusions

The presented modelling approach has been developed in the frame of IXV programme resulting into a key feature of the I/F design assessment at System level.

The adopted work logic resulted in an effective approach to:• Achieve the required detail level for I/Fs design justification• Reduce development times and iterations between the different

disciplines involved• Minimize and enhance data exchange cycles among several

analysis tools

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Improvements based on hybrid FEM/TLP analysis are being implemented to:

• Boost up detail level for I/Fs design refinement

• Further reduce development and coding endeavor (minimizing modeling mistakes)

• Enhance data exchange among several CAD/analysis suites

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Summary & Conclusions